Many advance fee fraud ("419") spam emails and all advance fee fraud letters contain a telephone number for contacting the sender. In most cases these involve mobile phones, but fixed lines are used too. Here is a small selection by country.

If an email mentions a UK phone number starting with +4470, it usually means that the sender of that mail is not in the UK at all and it is almost guaranteed to be a scam.

Usually the presence of a +44 70 number in a 419 scam email means you're dealing with criminals based in Nigeria who are using these numbers to make people believe they're dealing with someone legitimate who is in the UK instead of a criminal in an Internet cafe on a different continent.

Do not reply to any emails that mention +4470 phone numbers!

Never call such numbers!

Break off all contact with these people!

The scammer most likely is NOT based in the UK. +44 70 numbers belong to international call forwarding services. Their whole point is that people can reach the user of the number when he's not in the UK. These services make it possible for scammers to hide the fact that they are based in Nigeria or other countries in Africa, while the scam victim will believe they're dealing with someone in the UK. Very few (if any) legitimate individuals use these numbers. Banks, law offices, UK immigration officials, etc. never use +44 70 numbers because, since their offices are based in the UK, they have no need to redirect calls to their offices to some mobile phone outside the UK. We have not come across any legitimate UK businesses yet that use +44 70 numbers. Their only visible user base are scammers in Nigeria, South Africa and elsewhere. It is a perfect mystery to us why the UK authorities allow these services to continue operating despite them being used almost exclusively by criminals.

UK phone numbers starting with '70' are "Personal numbering" in the "Find me anywhere" range. Charges for calls to these numbers are not distance-dependent. They can cost as much as UKL 0.50 (USD 0.90) per minute to call and can forward the call to virtually any phone number in the world. Forwarding numbers can be set up for free and completely anonymously via websites such as uknumbers.com.

In most cases when you call one of these numbers the phone that starts ringing will actually be a mobile phone somewhere in Nigeria, as the UK number has been programmed to auto-forward calls to another number. These +44 70xx numbers are used as a redirector service to obscure the fact that the person taking the call is not actually based in Europe. The UK number is used to lend credibility to the scam. Unfortunately the authorities in the UK do not seem to be taking any action to shut down such phone numbers.

You can use the
UK Phone Number Locator
to find out what phone company the number is assigned to and the phone and email contact of the company where you can report the criminal abuse of their numbers.